The objective of passive acoustic systems designed for undersea surveillance and antisubmarine warfare (ASW) is to detect target-radiated acoustic signals in the presence of complex noise fields. The most advanced systems of this type today employ a combination of temporal gain achieved through narrowband signal-processing, and spatial gain, achieved through linear hydrophone arrays, to obtain a high level of performance. If it be true that the gains achievable through these means are now approaching a practical limit, then further improvement and performance will have to be obtained through other means, such as the use of multi-dimensional arrays.
The invention herein disclosed resulted from an effort to develop the technology required to form thinned planar and volumetric hydrophone arrays from fields of randomly placed, freely drifting, sonobuoys. The use of sonobuoys is intended to minimize the cost of such arrays, formerly thought to be prohibitive. It also allows the arrays to be readily deployed from a mobile platform, such as a long-range aircraft.
There are two basic issues that had to be resolved to demonstrate the feasibility of the random array concept. The first is whether the positions of the individual sensors of the array can be determined with sufficient accuracy for beamforming purposes. The second issue is whether the rate of dispersion of the sensors is sufficiently low to allow the array to be operated for a useful period of time. These two issues have been resolved satisfactorily.